The present invention relates to a printing head adopting an ink delivery technique effectively utilizing the capillary phenomenon of ink.
In the printing head of the above-noted type, namely an ink jet head, its ink guide passage for guiding ink and an ink jet opening for jetting ink therethrough are formed conventionally of a photosensitive glass or various ceramic materials.
It has been also suggested to provide the ink guide passage with ink-philic characteristics for improving ink deliverability while providing the ink jet opening with ink-phobic characteristics for restricting ink dripping.
However, if the ink guide passage and the jet opening are formed of an ink-philic resin, after an extended use the ink gradually penetrates the resin, and this penetrated ink eventually expands and deforms these portions. Further, the resin quality may be deteriorated by gradual development of mildew. This deformation and quality deterioration impairs stable and even ink jetting operation. In addition, if the jet opening is formed of ink-philic resin, there occurs disadvantageous dripping of excess ink at this portion.
On the other hand, if the ink guide passage and the jet opening are formed of a photosensitive glass, fine working is impossible because of poor resolution of photosensitive glass. Further, this does not eliminate the mildew development just as in the case with the use of resin.
With view to the above-described inconveniences, it has been also suggested to form the ink guide passage and ink jet opening of different materials by bonding these thereafter or to coat these portions with resin materials of different properties.
However, the bonding of different materials is very difficult and costly. The coating with different resins is also difficult because of the smallness and intricacy of these portions. Moreover, depending on the properties of employed resins, there occur the same inconveniences as described above.
Further, such materials as ceramics naturally have hydrophilic property which limits their use to water-based inks. Thus, if a ceramic material is used, an additional ink-phobic treatment will be effected on the leading end of the jet opening, whereby the same problems as above will occur again.
On the other hand, the ink delivery passage has PG,4 been formed by the cutting or etching method.
However, if such fragile material as a glass plate is cut, there tends to occur a cracking or chipping in the glass, which results in defective products and eventually a reduction in product yields. Moreover, if the ink passage is formed by the conventional cutting method, its interior wall face tends to be formed rough. Then, this rough surface causes pressure loss in ink passage thereby requiring large energy therefor and also deterioration in stability and evenness of ink delivery. On the other hand, if the ink passage formed e.g. of a glass plate is formed by the etching method, since the method is unsuitable for fine working, the same will disadvantageously limit the manufacturing precision.
In view of the above problems, in recent years, there has been an attempt to use a photosensitive resin for forming the ink passage.
However, if this photosensitive resin for forming the ink passage comprises conventional types such as novolak or polymethyl methacrylate, some problems remain. First, since it is difficult to form a thick coating pattern with a high aspect ratio and with a sharp edge, these photosensitive resin materials have never been put to actual use. Second, the conventional photosensitive resin materials are inferior in insulation and pressure-resistant characteristics and also readily subjected to expansion and deformation by ink penetration as is the case with the aforementioned other types of resin materials, thereby impairing the stable and even ink delivery.